Improve error handling and prevent panics during file processing

[digizeph]

Summary

• Replace unwrap()/expect() calls with proper error handling throughout the codebase
• Add clippy lints to prevent future panic-prone code
• Fix network error handling in multi-file processing operations

Key Changes

• Core library safety: All critical library functions now use Result types with descriptive error messages
• Network resilience: Failed remote file downloads no longer crash the entire search process
• Parallel processing: Individual file failures skip gracefully while other files continue processing
• CI improvements: Added formatting and clippy checks to enforce code quality

Files Modified

• Enhanced error handling in src/config.rs, src/database.rs, src/datasets/
• Fixed network error panics in src/bin/monocle.rs
• Updated CI workflow to include quality checks
• Added clippy deny rules for unwrap_used and expect_used

Core library now passes clippy checks with no warnings and builds successfully.

Resolves #75